The present invention relates to an infrared sensor adapted to be stabilised in temperature and an infrared thermometer with a sensor of this type, in particular, for temperature measurement in the ear.
DE 199 13 672 describes an infrared thermometer with a probe which includes an infrared wave guide and a radiation sensor arranged at the end thereof. The probe and/or a probe cover which is adapted to be mounted onto the probe in a per se known manner are/is so designed that only the front area of the probe or the probe cover can be heated to a temperature which roughly corresponds to the normal temperature in the ear canal. Because the infrared sensor disposed in the probe has an only limited field of view, it is sufficient for minimizing measuring faults that only that part of the probe has the same temperature as the ear canal which enters into thermal interaction with the part of the ear canal that lies in the field of view of the infrared sensor. The relatively small heatable area can be heated in an energy-saving fashion only if it is thermally insulated in relation to the non-heatable part of the probe, however, with the result that the design of the probe becomes more complicated.
GB 2090054 A discloses a radiation detector with a thermistor which is maintained at a constant temperature by two heating elements. The heating elements along with a mounting ring form an envelope which encompasses the thermistor. The envelope is encompassed by a casing having a window transparent to radiation, through which the radiation being detected is admitted into the casing and, through a hole in one of the heating elements, into the envelope and to the thermistor. This radiation detector necessitates a rather sophisticated manufacture and, hence, is quite expensive.
U.S. Pat. No. 5,010,315 discloses a heat radiation sensor element with two NTC resistors, the temperature of which is maintained constant by a respective heating layer. Insulating layers are interposed between the heating layers and the NTC resistors.
DD 147872 discloses a thermopile sensor with a casing that includes a window transparent to radiation. The casing accommodates a sensor element on a support member provided with a central bore which is covered by a membrane. The cold points and the warm points of the sensor element are placed on the membrane, namely the cold points in the area of the support member and the warm points in the area of the bore. Only the warm points are heatable by at least one heating element.
An object of the present invention is to provide a simple heatable and/or coolable infrared sensor and an infrared thermometer of an especially straightforward construction.
An infrared sensor of the present invention includes at least one infrared sensor element, one heating and/or cooling element, and a casing with a window transparent to infrared radiation. The window may e.g. be made of chalcogenit glass which is transparent to infrared radiation and easily formable. The sensor element is arranged in the casing so that infrared light is admitted through the window to the sensor element. The heating/cooling element is connected to the window and/or the casing in a heat-conducting way. It is especially favorable that the casing has such a design as to permit only low temperature gradients inside the casing. Therefore, the heating/cooling element is preferably arranged so that, in the heating or cooling process, the casing and the window will evenly be heated or cooled. To this end, the window and the casing are heat-conductingly interconnected and made of materials having a high degree of thermal conductance, e.g., the casing is made of copper and the window of silicon. There may also be provision of a plurality of heating/cooling elements, one or more of them being arranged on the casing and at least one other being arranged at the window of the infrared sensor. The term xe2x80x9cheating/cooling elementxe2x80x9d e.g. refers to a heating element configured as an NTC or PTC resistor or transistor and, also, a heating and cooling element configured as a Peltier element. Preferably, the heating/cooling element can be heated or cooled electrically.
The heating/cooling element is preferably fitted to the casing of the infrared sensor. It may also consist of a foil, for example, a polyimide foil, to which is applied a conductor-path shaped metal layer, e.g., from aluminum, copper, gold, or a chrome-nickel alloy, or a silver/graphite paste. A heating element which is e.g. made of a conductor-path shaped metal layer or a layer of an electrically conductive plastic material may also be applied directly to the window. In another embodiment of an infrared sensor of the present invention, the window can be heated by a heated filament of constantan, for example, which is passed around the window and has a good heat-conducting connection to it. In a particularly elegant design of an infrared sensor of the present invention, the window is comprised of a semiconductor, especially silicon, in which an electric conductor path made by doping is used as a resistance heating element.
The infrared sensor includes at least one temperature sensor which, preferably, has a heat-conducting connection to the infrared sensor element in a per se known manner. In another embodiment of an infrared sensor of the present invention, the heating/cooling element itself is used as a temperature sensor. When the infrared sensor element is a thermopile, the thermopile itself may serve as a temperature sensor in a way per se known from EP 0 502 277. In this event, the infrared sensor has connections for the infrared sensor element(s) and for the heating element(s). In case the heating element or infrared sensor element is not used as a temperature sensor as well, the infrared sensor additionally has connections for the temperature sensor. The temperature sensor is connectable to a control means by way of its connections.
The control means determines the temperature of the temperature sensor and, thus, of the infrared sensor as well from measurable characteristic magnitudes of the temperature sensor, heating/cooling element, or infrared sensor element, such as the electric resistance, the threshold voltage, or the forward voltage. Preferably, the control means includes for each heating/cooling element a control circuit which, in response to an adjustable nominal temperature value, delivers to the heating element(s) the energy that is respectively required for heating, cooling and/or maintaining the temperature constant. This way, the infrared sensor can be set to a defined temperature and stabilised in temperature. Further, the control means can be connected to an energy source, for example, a battery.
The control means may also be arranged in the infrared sensor which, in this event, apart from the connections for the infrared sensor element(s) includes connections for the input of a nominal temperature value and for connecting to an energy source.
The infrared sensor includes one or more infrared sensor elements, especially thermopiles, as generally disclosed in the relevant prior art. For example, EP 0 566 156 B1 discloses an infrared sensor with two infrared-sensitive elements, one of which is shielded against infrared radiation. A comparison of the signals sent by the two elements permits obtaining a measuring signal which corresponds to the quantity of the incident infrared radiation and is virtually free from electric noise and thermal disturbance. However, the infrared sensor element(s) may also have the design disclosed in DE 197 10 946.
In a preferred embodiment of an infrared sensor of the present invention, a plurality of infrared sensor elements are arranged like a matrix. In this event, the window of the infrared sensor is preferably designed as a lens. The infrared sensor elements are preferably disposed in the focal plane of the lens.
The infrared sensor is arranged directly at the front end of a probe in an infrared thermometer of the present invention. The advantage of this design involves that due to the heatable/coolable infrared sensor practically the entire front end of the probe, or at least the front surface of the probe, may be set to the desired temperature. Therefore, when the probe is introduced into the ear canal, the thermal balance in the ear canal is practically not disturbed, which avoids measuring faults. The probe may have a per se known shape or a per se known design; especially, it may be flexible. As an example for a probe of this type EP 0 588 631 A2 is referred to which describes a flexible probe having its flexibility increased by a slot or bellows provided on its outside periphery. Further, the probe may have ribs, indentations, or the like, on its outside.